The American philanthropist Bill Gates has said the key to stopping the Aids pandemic lies in giving women the power to protect themselves.

He was speaking at the opening of the 16th international conference on HIV and Aids, being held in Toronto.

The Gates Foundation has already given millions of dollars for Aids research.

It is now 25 years since Aids was recognised, but a vaccine for HIV remains elusive despite huge advances in drug treatment.

Organisers say there is an urgent need to extend access to drug treatment and methods of preventing HIV infection.

The numbers infected with the virus that causes the disease now tops 45m.

The epidemic continues to have its worst effect in the poorest countries.

Male circumcision is emerging as a promising potential method for preventing new infection and teams of researchers are trying to develop microbicides.

Progress

In his opening address, Mr Gates said his charitable foundation would be putting more money into developing drugs and microbicide creams that women could use before sex to prevent infection with HIV.

A woman should never need her partner's permission to save her own life

Bill Gates

He urged governments and other donors to join him in increasing funding for what he said could be the next big breakthrough in the fight against Aids.

"Obviously the Aids epidemic is going to require all actors, particularly governments, to dig deep and make this a high budgetary priority," he said, in remarks before the opening.

And he said progress in the development of microbicides offered real hope to millions of people: "A woman should never need her partner's permission to save her own life. There's progress on these, but the pace has been too slow."

His call was echoed by Stephen Lewis, UN special envoy on Aids in Africa: "To change the sexual behaviour of men is a question of generations. Women are dying now."

The organisers have defended the $20 million (£11m) cost of staging the event, which is being attended by 24,000 professionals, activists and journalists.

They say that money raised by sponsorship goes back into research and scholarship programmes.

The conference also heard from a Rwandan woman Laurance Mukamurangwa, who cares for five grandchildren aged three months to five years, despite being infected herself by HIV after she was raped.

She said: "It's really a problem for us because we don't have anything and must get food, clothes and school supplies and you must remember that I am sick too and I will die."